With regard to a mobile communication in which the state of data transmission path momentarily changes, there are valuable error control techniques, for example, ARQ (Automatic Repeat reQuest), that is, an automatic retransmission control, and an error correction code such as FEC (Forward Error Correction). ARQ is mainly provided as a function of MAC (Media Access Control) layer (MAC-ARQ). There are various types of ARQ methods, for example, the Stop-and-wait method, the Go-back-N method and the Selective-repeat method.
In the Stop-and-wait method, every time a transmission side transmits a packet, a reception side transmits a NACK (Negative ACKnowledgement) signal or an ACK (ACKnowledgement) signal. In addition, the transmission side retransmits the same packet as previously transmitted when receiving a NACK signal (retransmission request) and transmits a next packet when receiving an ACK signal. In the Go-back-N method, the transmission side successively transmits N packets. When receiving a retransmission request (HACK signal) from the reception side, the transmission side retransmits all packets including the packet which is requested to be retransmitted and the following packets. In Selective-repeat method, the transmission side successively transmits N packets. When receiving a retransmission request (NACK signal) from the reception side, the transmission side retransmits packets only if they are requested to be retransmitted.
[Patent Document 1] Japanese Patent Application, First Publication No. 2003-319464
With regard to the above-described MAC-ARQ, in order to accurately transmit a packet when retransmitting the packet to the reception side, there are cases in which the packet is retransmitted after switching a modulation method to another modulation method which has mow transmission rate, for example, BPSK (Binary Phase Shift Keying). In such a case, it is possible to increase the possibility to accurately transmit the packet which is retransmitted to the reception side, but there is a problem of low data throughput due to a low transmission rate.